The overall goal of this project is the identification of the major mechanisms which account for resistance of advanced colon cancers to high dose alkylating agents. To achieve this goal we plan to construct human colorectal cancer cell lines and xenograft models which are resistant and sensitive to BCNU and melphalan. We are in a strong position to pursue this work because we have developed a large bank of colon cancer derived cell lines which includes the diverse phenotypes that one anticipates would be found in a disease as heterogeneous as colon cancer. Since intrinsic resistance to these two alkylating agents is the major clinical problem, we will emphasize cell lines which have never been exposed to chemotherapy. Because acquired resistance may differ qualitatively from intrinsic resistance and may be relevant to the clinical resistance that is observed in the clinic with high dose alkylator therapy, we plan to develop additional cell line models with acquired resistance. Mutants with acquired resistance will be selected from intrinsically sensitive colon cancer cells and the paired sensitive parental and acquired resistant lines that are produced will be used by the collaborating projects in the program to characterize the levels of protein and gene expression required for certain resistant phenotypes and to evaluate modulation strategies. Finally, we will evaluate in vivo in athymic mice the selectivity of promising strategies to circumvent or modulate resistance.